As is well known, as civilian society has been developed, industries have highly developed and the trend is even rising.
For various equipments which support civilian society and industrial economy, it is required to maintain the inherent functions thereof not only at installation thereof but also over a sufficiently long period.
As chemical technology advances, most of those equipments comprise a plurality of parts to perform complex functions. Accordingly, the assembling and engagement structures are three-dimensional and complex. In order to sufficiently maintain the functions, periodic and non-periodic tests of the functions are essential in addition to the tests at new installation. Depending on actual status of use, a periodic test is legally obliged.
It is desirable to check those equipments at new installation as well as at the periodic or non-periodic function tests during use for the maintenance purpose, by disassembling them into individual parts or part units (hereinafter collectively referred to as parts). However, where the equipment has a complex assembling and engagement structure, the test by disassembling is very troublesome, and does not meet economical requirement, and lowers run efficiency. Under certain circumstances, the test by disassembling may impair the functions of the parts and hence nondestructive testing has been widely used.
Recently, because of the fact that many equipments are made of metals, the nondestructive testing by ultrasonic wave disclosed in JP-A-53-143293, JP-A-577691 and JP-A-62-21014 have been used widely.
Where a part of an equipment is a plane or of simple curved shape such as a pipe, an ultrasonic defect testing system is simple and little skill is required for the test. However, in the recent mechanical equipments for automobiles, ships, aeroplanes and generators, parts are widely used having a complex three-dimensional free curved surface such as a turbine blade, a pump casing, a main steam tube joint, a large size valve or a tube table. Among others, in nuclear facilities, medical facilities and laboratories, it is strongly demanded that those parts of the complex shapes maintain their functions almost perfectly for years. Because of the difficulty of the test by the disassembling, the ultrasonic defect testing of the parts having the complex three-dimensional free curved surfaces is demanded. It is also demanded to record and keep the defect data for subsequent use or for the study of elongation of the lifetime of the same or a similar type of equipment.
However, the ultrasonic defect testing for the part having such a complex three-dimensional free curved surface has an essential shortcoming which cannot be solved by the existing and practiced ultrasonic defect testing system for the part having a simple plane or curved surface.
Since a defect image cannot be superimposed on an image of a part, that is, an image representing a contour of an object under test, it is not possible to discriminate an echo reflected from the contour of the object to be tested from one reflected from the defect. Namely, where there is no image of the object under test, or where there is an image of the object but it includes outer surface corrosion, or where the object under test was not made as the same image as displayed, an optimum defect testing condition cannot be determined unless shapes of inner and outer surfaces are grasped, or it is not possible to decide whether an echo derived by the ultrasonic defect test is one reflected from the inner surface of the object under test or from the defect.
Specifically, the defect testing conditions include a defect testing approach position, a scanning direction, a refraction angle of a probe, an operating frequency of the probe, a dimension of a resonator of the probe, an orientation of the probe and scanning velocity.
An ultrasonic defect testing system for a part having free curved shape which utilizes laser technique and ranging technique by making use of computer technology in order to meet those needs has been developed but it does not still fully meet the inherent needs as is well known technically.
FIGS. 3 and 4 show a test in a system 2 which ultrasonically tests defects a, b and c at deep inner locations such as air bubbles and tear-off in an object 1 under test having a complex three-dimensional free curved surface such as a turbine blade. As shown in FIG. 3, a laser range finder 3 is mounted on a hand 4 of a robot as a probe to measure surface shape of the object 1 under test in the air. The robot hand 4 is driven by a six-axis synchronized drive unit 5 which is controlled by a personal computer 6 to measure the shape of the object 1 under test. The measurement data is processed by a mini-computer 7.
Then, the defects a, b and c of the object 1 under test are ultrasonically tested in the water by an ultrasonic defect testing apparatus 8. An operation of a probe is controlled by the mini-computer 7 which calculates paths on the basis of shape measurement data of the object 1 under test by use of the laser range finder 4. As shown in FIG. 4, an upper half of the object 1 under test is displayed as a rectangular image 10' on a screen 10 of the mini-computer 7. Defect images a', b' and c' corresponding to the defects a, b and c are shown in the image 10' of FIG. 4. Numeral 9 in FIG. 3 denotes an image analyzing unit for analyzing images the basis of the data from the ultrasonic defect testing apparatus and the data from the synchronous drive unit 5.
In the ultrasonic defect testing method for the deep defect zone of the object under test which has three-dimensional free curved surface shape in the prior art system, the three-dimensional defect testing to the deep defect zones of the object under test is basically the scanning by a probe which is done on the basis of the measurement of the outer free curved surface of the object under test. Accordingly, in actual, the image display 10' of the object under test shown in FIG. 4 is a plane display (depth is not displayed) and is not a three-dimensional display. Accordingly, the measurement of the relative position, the inclination and the size of the defect in the deep areas of the three-dimensional shape of the object under test, and data analysis by the probe are not attained. Further, because of mono-chromatic display, the discrimination performance is poor.
Because the display of the defect test image 10' is a rectangular developed image as shown in FIG. 4, the overall shape including the inner and outer three-dimensional shapes of the object under test is not displayed. Further, though the outer surface is displayed, the shape of the inner surface or the rear surface which include the defect are not measured.
Because of the two systems that the measurement is done in the air and that the defect testing is done in the water, working environments for the shape measurement and the defect testing are different. The mounting and the removal of the object 1 under test are very troublesome, and the adjustment is inconvenient and inefficient.
When the dipping status of the object 1 under test is not good and the application of water jet in front of and behind the object under test is not good, alternative process is very difficult to attain.
In the prior art method, since the defects of the object under test is ultrasonically tested while the object is immersed in the water, the object to be tested is limited to a ceramic product or a small object, and freedom of handling is low.
Further, since shapes of the inner and outer surfaces of the object under test are not measured, the image display on the screen is not three-dimensional and a propagation path of the ultrasonic wave cannot be analyzed. Accordingly, the defect testing condition for the three-dimensional shape of the object under test cannot be instantly determined.
In addition, because the measurement data cannot be displayed on the screen on real time basis, discrimination of the defects is not easy and not efficient.
Further, as described above in connection with the defect testing, it is difficult to discriminate the echo from the inner shape or the rear shape of the object under test from the echo from the inherent defect.
Further, since the beam is irradiated by the spotwise coordinate extraction when the shape measurement by the laser or the defect testing by the ultrasonic probe is to be conducted, the entire area cannot be simultaneously covered because of the size of the beam. Where the object under test includes fine unevenness, the shape measured by the laser does not match to the shape required for the ultrasonic defect testing, and the position and the direction of the probe are not determined. In addition to the spotwise coordinate extraction, the derived echo must be corrected. As a result, accurate processing is not attained.
Further, since the six-axis synchronous drive unit is used, the freedom of scanning of the probe and the freedom of the scanning area are small.
Further, since the object under test is displayed by the rectangular image display, the above leads to the disability of the three-dimensional discrimination and detection of the defect testing ultrasonic echo.